To prevent decay and quality deterioration of food products, preservatives are commonly added. For decades, chemically synthesized food preservatives have been the primary choice to achieve this goal. More recently, safety issues have been raised with respect to these chemically synthesized food preservatives. Ever since, there has been a growing interest in antimicrobial substances derived from traditional foods.
Lactic acid bacteria are useful microorganisms, which have been traditionally used in the production of various fermented food products. Lactic acid fermentation results in inhibition of the growth of other contaminating bacteria. Due to the pH reduction of the systems with lactic acid produced via lactic acid fermentation, decay and quality deterioration of such food products can be prevented and/or reduced. Additionally, it has been determined that certain additional antimicrobial substances, such as bacteriocins, are produced by some lactic acid bacteria. A known bacteriocin for the control of pathogens in food is nisin. Nisin is produced by Lactococcus lactis strains and inhibits a broad range of Gram-positive bacteria. These bacteriocins belong to the lantibiotics group (class I bacteriocins) and have a long history as food preservative.
It is becoming increasingly common to use lactic acid and nisin containing ferments produced by such strains as preservative agents in all kinds of food products.
Conventional bacteriocin fermentation methods are generally inefficient for nisin production on a large (commercial) scale due to limited production rates and unsatisfactory final nisin concentrations. Prolonging the fermentation process also inherently increases the risks of contamination of production batches. More importantly, slow nisin production rates make commercial nisin production costly. Another relevant cost factor is the relatively expensive fermentation medium requirements.
Nisin containing ferments are only exceptionally produced at the same plant where they are also applied to produce the final food products. In most instances nisin containing ferments will be manufactured at one plant to be used, typically some time later, at another plant in the production of the food product. The fermentation products therefore often need to be processed into formulations that can be stored for some time without loss of quality and/or activity, can be transported efficiently and are convenient to handle and to dose in the production of food products. For economic reasons it is often desirable to provide the products in concentrated forms. Such formulations may suitably be liquid, semi-liquid or solid type formulations, each type of formulation having its specific advantages and disadvantages. The most preferred choice will typically vary from one use to another.
The possibilities of producing stable and easy-to-use liquid, semi-liquids and/or solid formulations of nisin containing ferments are to a large extent determined by the thermodynamic behavior of the lactic acid salt(s), constituting the bulk of the ferment. This thermodynamic behavior sets the conditions required for downstream processing into the formulation type of choice, which conditions in turn may have significant impact on the nisin content/activity in the formulation.
Last but not least, organoleptic, dietary and food regulatory requirements additionally put restraints on the fermentation and down-stream processing steps and the types and amounts of the materials to be used therein.
In summary, manufacturers of nisin containing preservative compositions encounter a number of interrelated technological challenges to optimize the process and satisfy the needs and requirements imposed by specific (end-)uses of the product, in particular with regard to production rate and yield, stabilization of the activity, and the processing into stable and easy-to-use formulations. As will be understood, keeping the manufacturing costs at an acceptable level is always a factor in the design of the process.
It is an object of the invention to provide methods for producing nisin containing ferments and formulating such ferments into preservatives. It is in particular an object of the present invention to provide improved processes for producing nisin containing ferments by simple and efficient (batch) culturing and allowing for simple down-stream processing either into a liquid, semi-liquid or a dry powder product, having sufficient nisin content and stability, good handling properties and satisfactory organoleptic properties.